A Bluetooth® wireless radio protocol is used by Bluetooth-enabled wireless devices to establish a Bluetooth communication link using a short-range wireless connection. To establish a Bluetooth communication link, a first Bluetooth-enabled device attempting to establish a connection with a second Bluetooth-enabled device in the network, repeatedly broadcasts trigger signals which may include the unique device access code (DAC) of the second Bluetooth-enabled device. To establish a connection with requesting Bluetooth-enabled devices, the second Bluetooth-enabled device can periodically scan predefined radio frequencies within the 2.4 GHz (2.402 GHz and 2.480 GHz) industrial, scientific, and medical (ISM) radio band to listen for any trigger signals for the duration of a scanning time interval.
In a specific Bluetooth specification, the trigger signal may be transmitted at one of four possible trigger frequencies, 2402 MHz, 2425 MHz, 2450 MHz and 2480 MHz. If the second Bluetooth enabled device receives a trigger signal during a duration of the scanning time interval, the second Bluetooth enabled device can correlate the device access code included in the trigger signal against the unique access code of the second Bluetooth enabled device to determine if there is a positive correlation between the device access code received and the unique device access code of the second Bluetooth enabled device. If a positive correlation exists, a connection can be established between the first Bluetooth enabled device and the second Bluetooth enabled device.
Low power operation of a wireless radio device can be desirable in order to prolong the battery life of the device. In order to establish connections among Bluetooth enabled devices, one of the devices may periodically operate its radio receiver to open a scanning window to receive trigger signals which may or may not include its unique device access code. Operating the radio receiver to open the scanning window in order to establish a wireless connection may represent a significant portion of the power consumed by a Bluetooth enabled device.
In addition to Bluetooth devices, Wi-Fi or wireless local area networks (WLANs), operating under the IEEE 802.11 standard, also utilize the ISM radio frequency band for reception and transmission. As such, a Bluetooth device located in close proximity to a WLAN device can operate within the same radio frequency range while maximizing throughput and performance for both standards. Adaptive frequency hopping (AFH) is typically employed in the Bluetooth standard to mitigate radio interference in this common frequency band, thereby minimizing the possibility of performance degradation and improving the coexistence of the two standards. Bluetooth AFH uses a 1 MHz wide channel and a hop rate of 1600 hops/sec between the 2.4 to 2.4835 GHz, resulting in 79 different channels. Alternatively, WLAN IEEE 802.11 technology may use any of 11, 22 MHz-wide, subchannels allocated across 83.5 MHz of the 2.4 GHz frequency band.
Additionally, modern wireless devices may comprise both Bluetooth and WLAN functionality. Incorporation of a Bluetooth radio and a WLAN radio in a single device is commonly referred to as collocation. For example, Bluetooth and WLAN radios may be collocated devices such as mobile phones, laptops, personal digital assistants (PDAs), etc. In these devices, the Bluetooth radio and the WLAN radio may need to receive or transmit simultaneously. Collocation of the Bluetooth radio and the WLAN radio in a single device further increases the possibility of interference within the channel. It is desirable to minimize such interference resulting from the collocation of the two technologies on the same wireless device, thereby improving the coexistence of the two technology standards.